Abstract
Goals of this thesis were to determine if rainfall is a predictor of episodic changes in ammonia concentration in the River Lark downstream of Fornham St. Martin, UK; if there is a relationship between the ammonia concentration-discharge (C-Q) hysteresis patterns observed for storm events and the range of discharge per storm, total event rainfall, or antecedent catchment wetness; and to make inferences about the relative importance of different catchment ammonia sources for storm-related nutrient export during the growing season. Ammonia concentration in the River Lark was sampled at 30-minute intervals for several months during the 2021 growing season by the UK Environment Agency. These data and discharge were used for C-Q hysteresis analyses. An existing hysteresis index was adapted to quantify the total amount of C-Q hysteresis exhibited by storms with complex, figure-of-eight hysteresis patterns. Predominantly clockwise ammonia C-Q hysteresis was observed in the upper River Lark, indicating dilution from stormflow as the primary predictor of ammonia concentration. The constant input of effluent discharged from Sewage Treatment Works (STWs) appeared to be the most important source of ammonia in this part of the catchment during the growing season. However, some anti-clockwise hysteresis was observed during the two storm events with the heaviest rainfall, indicating that the dominant sources of ammonia in the catchment may vary seasonally.